Monocular vision is vision using only a single eye. It is seen in two distinct categories: either a species moves its eyes independently, or a species typically uses two eyes for vision, but is unable to use one due to circumstances such as injury.

Monocular vision can occur in both humans and animals (such as hammerhead sharks). Humans can benefit from several monocular cues when using only one eye, such as motion parallax and perspective. There are also some mythological creatures with only one eye, such as the cyclops.

Monocular vision is known as seeing and using only one eye in the human species. Depth perception in monocular vision is reduced compared to binocular vision, but still is active primarily due to accommodation of the eye and motion parallax. The word monocular comes from the Greek root, mono for single, and the Latin root, oculus for eye.

The eyes of an animal with monocular vision are positioned on opposite sides of the animal's head, giving it the ability to see two objects at once. This is usually most commonly seen with prey animals, as the reason why their eyes are placed on either side of their head is to make it easier for them to look out for predators, which usually have forward-facing eyes to make it easier to find prey. However, there are some exceptions to this rule, usually if the predator is an animal that is often preyed upon by a greater predator (because of this, apex predators usually tend to have forward-facing eyes) or sport an anatomy that makes it very difficult for it to see straight, such as a short, stiff neck that would limit its head movement, and therefore would require its eyes to be on either side (this is often seen with marine predators such as sharks and killer whales).

Notably, hammerhead sharks have some binocular vision as well as some amount of monocular vision.

Monocular vision impairment refers to having no vision in one eye with adequate vision in the other.

Monopsia is a medical condition in humans who cannot perceive depth even though their two eyes are medically normal, healthy, and spaced apart in a normal way. Vision that perceives three-dimensional depth requires more than parallax. In addition, the resolution of the two disparate images, though highly similar, must be simultaneous, subconscious, and complete. (After-images and "phantom" images are symptoms of incomplete visual resolution, even though the eyes themselves exhibit remarkable acuity.) A feature article in The New Yorker magazine published in early 2006 dealt with one individual in particular, who, learning to cope with her disability, eventually learned how to see three-dimensional depth in her daily life. Medical tests are available for determining monoptic conditions in humans.

Monocular cues provide depth information when viewing a scene with one eye.